Backlight unit and liquid crystal display unit using backlight unit

• US 20060044830A1
• Filed: 09/26/2003
• Published: 03/02/2006
• Est. Priority Date: 09/30/2002
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Shimizu, Masaki, Inoue, Yutaka, Ohtsuka, Kohji, Yoshii, Takashi, Idei, Kazuya
• Granted Patent: US 7,446,829 B2
• Time in Patent Office: Days
• US Class Current: 362/614
• CPC Class Codes: G02B 5/021 the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02B 5/08 Mirrors vehicle mirrors involving special optical features B60R1/08
• CPC Class Codes: G02F 1/133604 with lamps
• CPC Class Codes: G02F 1/133611 including means for improving the brightness uniformity

Abstract

To compensate for uneven brightness in the longitudinal direction of fluorescent lamps of a backlight unit and achieve a display screen with an even brightness, a reflection unit of the backlight unit, the fluorescent tube surface of the fluorescent lamps or a diffusion unit is used to either reduce the reflectance, transmittance, or radiation brightness of the high-voltage side of the fluorescent lamps or increase the reflectance, transmittance, or radiation brightness of the low-voltage side thereof so as to compensate for uneven brightness of the illumination light and thereby ensure an even brightness. For example, dot pattern regions D₁, D₂ and D₃, i.e., the regions whose density increases in stages, are imparted to the portion of a reflection layer 13 of the backlight unit with a relatively high brightness. As for the display device, on the other hand, the display image data supplied to a liquid crystal panel or the aperture ratio of the liquid crystal panel is controlled, for example, to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps and ensure an even brightness.

Claims

1. A backlight unit operable to illuminate the target with fluorescent lamps, the backlight unit comprising brightness compensation means adapted to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

2. The backlight unit of claim 1 comprising a reflection portion adapted to emit the light from the fluorescent lamps in a specific direction, wherein the brightness compensation means are provided on the reflection unit and control the reflectance of the reflection portion to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

3. The backlight unit of claim 2, wherein the brightness compensation means have regions with relatively high and low reflectances in the reflection portion and take advantage of the difference in reflectance to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

4. The backlight unit of claim 3, wherein the brightness compensation means have a reflectance gradient that causes the reflectance of the reflection portion to decline gradually or in stages and take advantage of the reflectance gradient to reduce the brightness of the portion with a relatively high brightness in the longitudinal direction of the fluorescent lamps.

5. The backlight unit of claim 3 or 4, wherein the brightness compensation means have a reflectance gradient that causes the reflectance of the reflection portion to increase gradually or in stages and take advantage of the reflectance gradient to increase the brightness of the portion with a relatively low brightness in the longitudinal direction of the fluorescent lamps.

6. The backlight unit of any one of claims 2 to 5, wherein the brightness compensation means are a dot pattern provided on the reflection portion and take advantage of the dot pattern to control the reflectance of the reflection portion.

7. The backlight unit of claim 6, wherein the reflectance of the reflection portion provided with the dot pattern is controlled by one or a plurality of the reflectance of the group of small dots making up the dot pattern, the dot density, the dot shape, and the dot color.

8. The backlight unit of claim 1 comprising a reflection portion adapted to emit the light from the fluorescent lamps in a specific direction, wherein the reflection portion is made up of first and second reflection layers having given optical reflectance and transmittance levels, wherein the reflection portion is configured with a first region having the first and second reflection layers stacked one above another in the direction of incidence of light and a second region made up only of the first reflection layer, and wherein the reflectance of the reflection portion is controlled using the first region with a relatively high reflectance and the second region with a reflectance lower than that of the first region.

9. The backlight unit of claim 1, wherein the brightness compensation means are provided on a glass tube of the fluorescent lamps and control the transmittance of the glass tube to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

10. The backlight unit of claim 1 comprising a diffusion portion adapted to diffuse the light from the fluorescent lamps, wherein the brightness compensation means are provided on the diffusion portion and control the transmittance of the diffusion portion to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

11. The backlight unit of claim 9 or 10, wherein the brightness compensation means have regions with relatively high and low transmittances in the glass tube or the diffusion portion and take advantage of the difference in the transmittance to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

12. The backlight unit of claim 11, wherein the brightness compensation means have a transmittance gradient that causes the transmittance to decline gradually or in stages and take advantage of the transmittance gradient to reduce the brightness of the portion with a relatively high brightness in the longitudinal direction of the fluorescent lamps.

13. The backlight unit of claim 11 or 12, wherein the brightness compensation means have a transmittance gradient that causes the transmittance to increase gradually or in stages and take advantage of the transmittance gradient to increase the brightness of the portion with a relatively low brightness in the longitudinal direction of the fluorescent lamps.

14. The backlight unit of any one of claims 9 to 13, wherein the brightness compensation means are a dot pattern provided on the glass tube of the fluorescent lamps or the diffusion portion and take advantage of the dot pattern to control the transmittance.

15. The backlight unit of claim 14, wherein the transmittance of the glass tube or the diffusion portion provided with the dot pattern is controlled by one or a plurality of the reflectance of the group of small dots making up the dot pattern, the dot density, the dot shape, and the dot color.

16. The backlight unit of claim 1, wherein the brightness compensation means are provided on the glass tube of the fluorescent lamps and control the tube surface brightness of the glass tube to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

17. The backlight unit of claim 16, wherein the thickness of the fluorescent substance formed inside the glass tube of the fluorescent lamps as the brightness compensation means is changed correspondingly with the longitudinal position of the fluorescent lamps to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

18. A liquid crystal display device comprising the backlight unit of any one of claims 1 to 17 and a liquid crystal panel illuminated by the backlight unit.

19. A liquid crystal display device operable to apply an illumination light from a backlight unit having fluorescent lamps to a liquid crystal panel to display images, the liquid crystal display device comprising brightness compensation means adapted to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

20. The liquid crystal display device of claim 19, wherein the brightness compensation means have a gradation conversion portion operable to carry out a given gradation conversion process of input image data and a control portion operable to switch between gradation conversion characteristics of the gradation conversion portion based on a synchronizing signal of the input image data, and wherein the control portion switches from one gradation conversion characteristic to another in the gradation conversion portion based on the screen position to display the image data to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.

21. The liquid crystal display device of claim 19, wherein the liquid crystal panel is configured to have, as the brightness compensation means, an aperture ratio that changes correspondingly with the display screen position, and wherein the aperture ratio is changed to compensate for uneven brightness in the longitudinal direction of the fluorescent lamps.